The present invention relates to valves for regulating chamber pressures of process chambers used in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to multi-unit pressure control valves for the rapid and accurate attainment of interior chamber gas pressures of process chambers such as etch chambers and CVD chambers.
Integrated circuits are formed on a semiconductor substrate, which is typically composed of silicon. Such formation of integrated circuits involves sequentially forming or depositing multiple electrically conductive and insulative layers in or on the substrate. Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer. CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both.
After the material layers are formed on the wafer substrate, etching processes may be used to form geometric patterns in the layers or vias for electrical contact between the layers. Etching processes include xe2x80x9cwetxe2x80x9d etching, in which one or more chemical reagents are brought into direct contact with the substrate, and xe2x80x9cdryxe2x80x9d etching, such as plasma etching. Various types of plasma etching processes are known in the art, including plasma etching, reactive ion (RI) etching and reactive ion beam etching. In each of these plasma processes, a gas is first introduced into a reaction chamber and then plasma is generated from the gas. This is accomplished by dissociation of the gas into ions, free radicals and electrons by using an RF (radio frequency) generator, which includes one or more electrodes. The electrodes are accelerated in an electric field generated by the electrodes, and the energized electrons strike gas molecules to form additional ions, free radicals and electrons, which strike additional gas molecules, and the plasma eventually becomes self-sustaining. The ions, free radicals and electrons in the plasma react chemically with the layer material on the semiconductor wafer to form residual products which leave the wafer surface and thus, etch the material from the wafer.
Referring to the schematic of FIG. 1, an etch reactor 30, such as an eMax etch reactor available from Applied Materials, Inc. of Santa Clara, Calif., includes a grounded reaction chamber 32, typically fitted with liners (not shown) to protect the interior wall surfaces thereof. A wafer 34 is inserted into the chamber 32 typically through a slit valve opening 36 and is placed on a cathode pedestal 38 having an electrostatic chuck 40 that clamps the wafer 34 in place. A cooling fluid circulates through cooling channels (not shown) in the pedestal 38 to control the temperature of the pedestal 38, and thus, the temperature of the wafer 34. A thermal transfer gas such as helium may be supplied to grooves (not shown) provided in the upper, wafer-supporting surface of the pedestal 38. The thermal transfer gas enhances the efficiency of thermal coupling between the pedestal 38 and the wafer 34.
An RF power supply 42 is connected to the cathode pedestal 38 and generates the etchant plasma while controlling the DC self-bias. Magnetic coils 44 encircle the chamber 32 and generate a slowly-rotating, horizontal, essentially DC magnetic field to increase the intensity of the plasma. A vacuum pump 46 pumps the gaseous contents of the chamber 32 through an adjustable throttle valve 48. Shields 50, 52 may serve to both protect the chamber 32 and pedestal 38 from the etchant plasma and define a pumping channel 54 connected to the throttle valve 48.
Processing gases are supplied from gas sources 58, 60, 62 through respective mass flow controllers 64, 66, 68 to a quartz gas distribution plate 70 positioned in the top of the chamber 32 overlying and separated from the wafer 34 across a processing region 72. The gas distribution plate 70 includes a manifold 74 that receives the processing gas and communicates with the processing region 72 through a showerhead having a large number of distributed apertures 76 which facilitate a substantially uniform flow of processing gas into the processing region 72.
By regulating the flow of gases from the interior of the vacuum chamber 32 to the vacuum pump 46, the throttle valve 48 of the etch reactor 30 is typically used to control the interior pressures of the chamber 32. As shown in FIGS. 2 and 3, the throttle valve 48 typically contains a valve frame 78 having a circular valve opening 79. A pair of adjacent valve blades 80 is pivotally mounted in the valve opening 79, and each of the valve blades 80 is operably engaged by a stepper motor (not shown). As shown in FIG. 2, in the closed position the valve blades 80 are disposed in coplanar relationship to each other and interlock to close the valve opening 79. As shown in FIG. 3, upon flow of gases 81 from the vacuum chamber 32 to the vacuum pump 46, the valve blades 80 are pivoted from the coplanar configuration to angled positions in stepwise fashion, thereby opening the valve opening 79 to varying degrees and regulating the rate of flow of the gas from the vacuum chamber 32 to the vacuum pump 46, and thus, the interior pressure of the chamber 32. The valve blades 80 can typically be incrementally opened throughout a range of finely-graded xe2x80x9cstepsxe2x80x9d from 0 (in which the valve blades 80 are disposed in substantially coplanar relationship, or 0 degrees, with respect to the planar surface 82 of the valve frame 78), through 800 (in which the valve blades 80 are disposed at a substantially 90-degree angle with respect to the planar surface 82). The xe2x80x9c0xe2x80x9d step corresponds to the configuration of the valve blades 80 at which the valve opening 79 presents no area for gas flow, whereas the xe2x80x9c800xe2x80x9d step corresponds to the configuration of the valve blades 80 at which the valve opening 79 presents the largest area for gas flow through the throttle valve 48.
Referring next to the graph of FIG. 4, wherein the area of the valve opening 79 available for flow of gas through the throttle valve 48 is plotted on the Y axis as a function of the various step positions of the valve blades 80, which are plotted along the x axis. It can be seen from the graph that a typical etch process is carried out in the chamber 32 when the valve blades 80 are between steps 10 and 45. In this relatively narrow process region interval, which begins when the valve blades 80 are close to the 0-step position, PI is aggressive and pressures in the chamber 32 are optimal for the etch process; on either side of the process region interval, pressures in the chamber 32 fluctuate rapidly and are unstable. Accordingly, a throttle valve is needed which is characterized by a wider process region interval that begins at a higher valve blade step to enhance pressure stability and maintain aggressive PI over a broader valve blade step range to increase throughput of wafers through the chamber and prolong hardware lifetime.
An object of the present invention is to provide new and improved blades for a throttle valve used in conjunction with a process chamber for substrate processing.
Another object of the present invention is to provide new and improved throttle valve blades which facilitate a broader process interval for the processing of substrates.
Still another object of the present invention is to provide new and improved throttle valve blades which enhance stability in chamber pressures during the processing of substrates.
Yet another object of the present invention is to provide new and improved throttle valve blades which maintain aggressive PI throughout a broader operational range of a process chamber for substrates.
A still further object of the present invention is to provide new and improved throttle valve blades for a throttle valve on a process chamber, which throttle valve blades increase tool throughput.
Yet another object of the present invention is to provide new and improved throttle valve blades which include notches provided therein to facilitate delayed onset and gradual variations in the rate of gas flow through a throttle valve throughout the step range of the valve blades.
Still another object of the present invention is to provide new and improved throttle valve blades the radius of which may be varied to facilitate delayed onset and gradual variations in the rate of gas flow through a throttle valve.
In accordance with these and other objects and advantages, the present invention is generally directed to new and improved valve blades for a throttle valve which is typically used to control gas pressures in a process chamber for substrates. The valve blades of the present invention facilitate delayed onset and gradual or fine variations in the flow of gas through the throttle valve to achieve a process interval of interior chamber gas pressures over a broader valve blade step range, achieve aggressive PI over a broad range for enhanced tool throughput, enhance stability of interior chamber gas pressures during substrate processing, and increase tool uptime and production efficiency. In one embodiment, each of the two valve blades in the throttle valve includes at least one, and typically, multiple notches or gaps for a delayed onset, and finely-graded increase, in flow of gas through the valve throughout the step range of the valve blades. The notches or gaps may have a rectangular cross-section or a triangular cross-section.
In another embodiment, the semicircular valve blades have a cam-shaped configuration and are capable of varying the radius of the circle defined by the two blades as the blades are stepped between the closed and fully-opened positions. Due to the unique configuration of the valve blades, flow of gas through the throttle valve is characterized by delayed onset of gas flow through the valve upon initial stepped opening of the valve blades, as well as gradual or finely-graded increases in flow of the gas through the throttle valve throughout the process interval to enhance pressure stabilization, tool uptime and production capability.